Open-loop motor speed control with LabVIEW

An open-loop dc motor speed control system is developed using National Instrument's Data Acquisition (DAQ) Board (Model 6040E) and LabVIEW software package. Pulse Width Modulation (PWM) technique is employed to control motor speed. A vi (virtual instrument) is developed with LabVIEW that allows the DAQ to read a user selected reference voltage continuously. The vi also generates a suitable triangular wave that with the help of the reference signal produces the desired PWM signal. PWM is an analog signal that switches between two predefined limits. The switching interval of the PWM controled by the reference signal determines the average power delivered to the motor circuit. The PWM signal is sent through the output port of the DAQ by the vi which in turn controls the motor speed. User from the front panel of the vi may input the amplitude and the frequency of the triangular wave, sampling rate of the reference signal, and the desired amplitude of the PWM. As the reference voltage increases, the width of the PWM (duty cycle) increases which in turn increases the speed of the motor. The varying nature of the motor speed is demonstrated in the laboratory by changing the reference signal. The principle developed in this project will be utilized in future endeavor toward controlling robot motion remotely via Internet.